1. Field of the Invention
The invention relates to an apparatus for treating a fibrous web, in particular a paper, board or tissue web, having a press section and a drying section.
2. Description of the Related Art
In order to express water from fibrous webs, central-roll press arrangements are often used. The fibrous or paper web is transferred to a smooth central roll from an impermeable dewatering medium, for example a felt. Further pressing in an additional nip is carried out on the smooth central roll. One example of such a press is what is known as the “DuoCentri-II” press. This can also be provided with a shoe press nip as a preceding nip or as the last nip. In order to remove the paper web into the drying section following the latter, a free draw is necessary, in which the paper web is drawn onto the first dryer fabric, unsupported by a clothing medium. In such a free draw, a web break often occurs.
In order to avoid such web breaks, solutions have already been specified in which the web is led to the drying section supported by an impermeable belt. In this case, the impermeable belt, that is to say the central belt, as it is known, wraps around the central roll. Since absolute impermeability cannot be achieved, in many cases, the belt can also have a residual permeability of, for example, about 10 cfm.
One disadvantage of this solution is that the critical point for any possible web breaks is merely displaced from the central roll into the drying section. Breaks thus often occur in the leading region of the drying section.
What is needed in the art is an effective way to avoid or reduce web breaks.